npmのヘルプを見てたら、installの右隣に「isntall」があってなんだこれはと思ったら、installのエイリアスだったみたいです。
installをタイプミスして「isntall」と入力してもエラーにならずに、ライブラリーがインストール出来るように配慮されているみたいですね。
$ npm -h
Usage: npm <command>
where <command> is one of:
add-user, adduser, apihelp, author, bin, bugs, c, cache,
completion, config, ddp, dedupe, deprecate, docs, edit,
explore, faq, find, find-dupes, get, help, help-search,
home, i, info, init, install, isntall, issues, la, link,
list, ll, ln, login, ls, outdated, owner, pack, prefix,
prune, publish, r, rb, rebuild, remove, repo, restart, rm,
root, run-script, s, se, search, set, show, shrinkwrap,
star, stars, start, stop, submodule, tag, test, tst, un,
uninstall, unlink, unpublish, unstar, up, update, v,
version, view, whoami
npm <cmd> -h quick help on <cmd>
npm -l display full usage info
npm faq commonly asked questions
npm help <term> search for help on <term>
npm help npm involved overview
Specify configs in the ini-formatted file:
/Users/daichi/.npmrc
or on the command line via: npm <command> --key value
Config info can be viewed via: npm help config
npm@1.4.3 /Users/daichi/.nvm/v0.10.26/lib/node_modules/npm